The Great Recession has upended the American tradition of moving to greener pastures. Instead of moving to a bigger home or for a higher-paying job, more Americans moved because they can't afford to stay where they are.

During the 2007-09 recession, 9% of Americans — about 4 million — moved locally, the highest level in a decade. And a growing number moved to cheaper housing or doubled up with family and friends, according to an analysis out Wednesday of Census data through 2010.

By contrast, moves across county and state lines declined.

People moved the most in metropolitan areas with the highest unemployment and highest foreclosure rates, particularly in hard-hit parts of the Sun Belt, shows research by US2010, a project funded by the Russell Sage Foundation and Brown University that examines changes in American society.

In Las Vegas, for example, one in five people moved locally during the recession.

"Typically, over the last couple of decades, when Americans moved, they moved to improve their lives," says Michael Stoll, author of the research and chairman of UCLA's public policy department. "This is the shock: For the first time, Americans are moving for downward economic mobility. Either they lost their house or can't afford where they're renting currently or needed to save money.

At the peak of the recession, falling fortunes was a prime reason for moving. Before the economy tanked, 41.3% moved locally to own a home or settle in a better neighborhood. During the recession, only 30.4% moved for those reasons. By contrast, more than 23% moved for cheaper housing during the recession, up from 20.8% before the bad times.

The theme song of The Jeffersons, a hit TV show in the 1970s about a black family that makes it big in the dry cleaning business and moves from Queens to Manhattan's East Side, is aptly titled Movin' On Up.

Yet this economic downturn has taken a disproportionate toll on the upward mobility of African Americans, the research shows.

"Most distressing is the evidence that black residents have been particularly affected by this trend — more likely to be pushed into a short-distance move by these economic conditions," Stoll says. "Blacks may have had less savings, fewer family members who could contribute, onerous debt from refinancing or subprime mortgages or greater expenses."

Unemployment and foreclosure rates are higher among blacks than whites.

"It's going to be years before (blacks) return to their pre-recession trajectory," says Roderick Harrison, a demographer at Howard University in Washington, D.C. "It's going to take a job, probably several months or years working at that job to maybe return to their own apartment or to get back into home ownership."